Fig. 2: Pump-probe characterization of exciton funneling under local strain gradient.

a Schematic of excitation points (top), measured excitation maps (second row), and measured emission maps (third row) from flat WSe₂ (left) and wrinkled WSe₂ excited at valley (center) and apex (right). The size of the excitation/emission maps is 8 × 8 μm². b Measured PL spectra of wrinkled WSe₂ with excitation fixed at valley and emission detected from valley to adjacent apex. The distance from 1 (valley) to 6 is 2.5 μm with 6 being apex, and the spacing between consecutive numbers is 0.5 μm. c Emission characteristics of funneling excitons in terms of measured PL peak intensity (black), measured fluorescence (area integrated PL; red), and measured PL peak wavelength (right y-axis; blue). d Pump-probe measurements of wrinkled WSe₂ with different pumping position and local strain distribution. (i)–(iii) maps were measured in a same sample with varying the pumping spots. The asymmetric strain in (iv) was 0.63% (left apex) and 1.28% (right apex), while weak strain in (v) was 0.81% on both side apexes. Scale bar, 1 μm. e Comparison of pump-probe funneling efficiencies in various material systems. Energy gradient was created by strain (this work (black) and nanoindented WSe₂ (red)²⁵) or electric field (interlayer exciton in MoS₂/WSe₂ heterostructure (blue)¹² and GaAs/AlAs coupled quantum well (green)⁴³).